The present invention generally relates to flexible magnets with an induced ANISOTROPY, and in particular to flexible anisotropic magnets made by thermal spraying.
Flexible magnets are used widely in electromechanical devices, e.g., generators, relays, motors, and magnetos; electronic applications, e.g., loudspeakers, travel-wave tubes, and telephone ringers and receivers; antitheft tags; holding devices, such as door closers, seals, and latches; and magnetic recording devices. Flexible magnets have been widely used in many applications because of desirable properties, such as good plasticity or resiliency and superior workability. These desirable properties are not found in hard magnets, such as sintered ferrite magnets or alloy magnets. However, the magnetic properties of such magnets have not been satisfactory because they are generally produced by blending a pulverized magnetic material with a rubber or plastic matrix. For example, prior art flexible magnets generally do not have a high enough energy product, i.e., the product of the coercivity and the remnant magnetization, which necessitates the use of larger magnets than that of the conventional sintered magnet for the same application. Accordingly, applications for flexible magnets have been restricted.
Furthermore, prior art flexible magnets are typically made by mixing substantially domain-size particles of a hexaferrite with a flexible binder and then shaping the mixture, typically by extrusion. The resulting free standing flexible magnets are limited in shape or form to long strips that must be cut down to size for practical use. In addition, flexible magnets produced from such processes can only be attached to a surface/substrate by undergoing another production step of using an additional fixing agent, such as an adhesive. Lastly, prior art flexible magnets are produced by using volatile organic compounds (VOC""s) as the solvent. The use of such VOC""s are environmentally hazardous, and the presence of VOC""s is not desirable during the production process or in the final product.
The critical factors for improving magnetic properties of flexible magnets are as follows: (1) maximizing the magnetic particulate content in the matrix material; (2) maximizing the orientation of the magnetic particles in the matrix material in a desired direction; and (3) maximizing the energy product, i.e., the product of the coercivity and the remnant magnitization.
Accordingly, there exists a need in the art for a cost-effective method for efficiently making a flexible magnet having (i) an induced magnetocrystalline anisotropy, and (ii) complex geometric shapes which cannot be achieved by an extrusion process. There also exists a need for an efficient method to provide a substrate with a flexible anistropic magnetic coating without the need for adhesives. Finally, there also exists a need for a substantially VOC free process for making flexible magnets.
The present invention encompasses a method for producing a flexible anisotropic magnetic coating onto a substrate. The method includes the step of thermal spraying a first spray stream of composite particles, which include magnetic particles incorporated into or onto a matrix material. The thermal spraying step is conducted at a temperature that is above the glass transition or melting point temperature of the matrix material, and a magnetic field is applied across the substrate. In one embodiment, the method further includes at least one additional spray stream of a magneto-fluid mixture. The at least one additional spray stream is combined with the first spray stream to coat the substrate. These novel methods provide magnetically coated substrates which exhibit magnetocrystalline anisotropy.
In another embodiment, a flexible, free standing, complex three-dimensional anisotropic magnet is provided by substituting the substrate with a removable mold in the above-described method. These flexible anisotropic magnets have magnetic particles dispersed within a matrix material.